1. Technical Field
The present invention relates a sheet adsorption device, a transport device using the sheet adsorption device, and an image forming apparatus using the sheet adsorption device and the transport device.
2. Related Art
As devices that adsorb a sheet such as a recording medium, devices that adsorb one surface of a sheet by using a negative pressure generating unit have been known. In addition, devices using a method of pressing a sheet by using a unit using an electrostatic force, a magnet, or the like have been known.
A device that adsorbs a sheet by using the negative pressure generating unit has an advantage that affect of static electricity for electric components is small. In addition, since the device does not have a magnet or the like on one surface of a sheet, there are advantages that almost the entire area of one surface of the sheet can be used for a print operation and the like.
An adsorption unit that performs an suction operation through an air hole formed on a support plate by using a negative pressure generating unit with a porous belt having a adsorption surface, on which a plurality of air holes is formed, moved on a support plate having a plurality of holes and fixing a recording medium to the adsorption surface having the holes has been known (for example, see Japanese Patent 3707640 (pages 4 to 5, FIG. 3).
When a suction operation is performed by using all the plurality of air holes all the time, the ratio of air holes covered with a recording medium to air holes not covered with the recording medium is changed in a case where the size of the recording medium located on the adsorption surface having the holes changes. Accordingly, a stable adsorption effect cannot be acquired, or noise increases due to generation of an airflow. Thus, the adsorption surface having a plurality of holes corresponding to the size of the recording medium is disposed in the porous belt in advance.
When the size of a recording medium does not correspond to the adsorption surface having the holes which is disposed in advance or a recording medium is deviated from the adsorption surface having the holes due to tilt of the recording medium, a stable adsorption effect cannot be acquired, or an air flow is generated so as to increase noise. In addition, the load of the negative generating unit changes, and accordingly, redundant power is needed.